Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$66.53	4.364%	$69.4334	$69.43	$69.45	$69.40
Purchase #2	$118.94	9.655%	$130.4237	$130.42	$130.40	$130.40
Purchase #3	$83.84	6.810%	$89.5495	$89.55	$89.55	$89.50
Purchase #4	$118.84	13.499%	$134.8822	$134.88	$134.90	$134.90
Purchase #5	$133.34	9.356%	$145.8153	$145.82	$145.80	$145.80
Purchase #6	$31.28	12.203%	$35.0971	$35.10	$35.10	$35.10
Purchase #7	$131.71	9.115%	$143.7154	$143.72	$143.70	$143.70
7 purchase totals =	$684.48		$748.9166	$748.92	$748.90	$748.80